The abuse liability of psychostimulants is well established and represents a significant public health concern. Unfortunately effective therapeutic strategies for psychostimulant abuse are sorely lacking since, at the cellular level, their mechanism of action is not well understood. Recent investigations by our group have revealed a vital role for the scaffolding protein beta-arrestin-2 and the Akt/GSK3 signaling pathway in mediating responses to psychostimulant drugs in vivo (Beaulieu et al., 2007 Cell). Through the execution of two complimentary aims, I will define the role of beta- arrestin-2 in the actions of psychostimulant drugs in the direct versus indirect pathways of the basal ganglia. In Specific Aim 1 I will generate novel transgenic mouse lines to facilitate the isolation of beta-arrestin-2 signaling complexes in direct and indirect pathways in vivo. Although previous work demonstrated the formation of beta-arrestin-2 signaling complexes in mixed populations of striatal medium spiny neurons (MSNs), our working hypothesis is that beta-arrestin-2-mediated signaling is differentially engaged by psychostimulants in direct versus indirect pathway-projecting MSNs thereby impacting dopamine-associated behaviors. The generation of the proposed transgenic line will enable the identification of pathway-specific biochemical processes that could not be resolved from the previous method. In Specific Aim 2 I will make use of the novel transgenic mouse lines proposed in Aim 1 to isolate distinct beta-arrestin-2 signaling complexes in direct versus indirect pathway- projecting MSNs in response to select psychostimulant drugs. By monitoring beta-arrestin-2 function in vivo I expect to elucidate common mechanisms that are central to the expression of dopamine- mediated behaviors. As such, this work promises to significantly advance our understanding of the signaling mechanisms employed by psychostimulant drugs and to identify novel pharmacological targets for a wide range of disorders involving dysfunction of the dopamine system.